I bought three Picoscope 3424 units recently. I was quite dismayed to notice that the residual noise of these units is quite big. On all of my units there seems to be random noise with amplitudes ranging between 5 and 8 resolution steps (Inputs shorted). With the units set to +-5 volt range, these steps are 2.44mV each so the noise has an approximate vallue of up to 20mV P-P. 8 Resolution steps represents 3 bits of the available 12, effectively reducing the instrument to a 9 bit device.
I tried to find some noise specs for these units in the product specification but could not find any.